Brachytherapy as used herein is defined as therapy performed on mammals in which radioactive sources are brought in the near vicinity of tissue to be treated. Conventionally the tissue to be treated was mainly cancerous tissue. Since the early nineteen nineties a new field has started using brachytherapy, namely endovascular brachytherapy of blood vessels that have been subjected to angioplasty. It has been discovered that irradiation of the angioplasty site before, during or after the performance of the angioplasty may significantly reduce restenosis of the site. Restenosis is the re-occlusion of a vessel due to tissue growth and vessel remodeling after the angioplasty procedure. Endovascular brachytherapy has been described in Bertrand, O. F. et al; Intravascular radiation therapy in atherosclerotic disease: promises and premises; European Heart Journal, (1997) 18, pag. 1385-1395; Diamond, D. A. et al; The Role of Radiation Therapy in the Management of Vascular Restenosis. Part II. Radiation Techniques and Results; JVIR (1998)9, pag. 389-400; Baumgart, D. et al; Die intravasale Strahlenbehandlung zur kombinierten Therapie und Prävention der Restenosierung; Herz 1977;22:335-346(Nr.6); Baiter, S.; Endovascular Brachytherapy: Physics and Technology; Catheterization and Cardiovascular Diagnosis 45:292-298(1998) and Nath, R. et al; Intravascular brachytherapy physics: Report of the AAPM Radiation Therapy Committee Task group No. 60; Med. Phys. 26(2), February 1999, pag. 119-152, Ron Waksman (ed): Vascular Brachytherapy, Second Edition, Future Publishing Company, Inc, 1999, Armonk, N.Y. and Waksman, R. et al: Vascular Brachytherapy, Nucletron B. V., 1996, Veenendaal, the Netherlands.
In various applications of brachytherapy a radioactive brachytherapy source is brought into the vicinity of the tissue to be treated through a tube like device such as a catheter. Such a tube like device is also known as a guide tube.
Radioactive brachytherapy sources have been described in a number of patents and other references. An exemplary embodiment of such description is known from U.S. Pat. No. 4,861,520. The source described therein comprises a steel capsule. An opening of the capsule is welded to a plug. The plug is welded in turn to a steel cable. Inside the capsule a number of radioactive iridium-192 pellets is present.
Another exemplary embodiment of a radioactive brachytherapy source may be found in U.S. Pat. No. 5,084,001. Therein is shown and described a relatively pure platinum wire with near one of its tips a rod like piece of iridium-192 fully encapsulated by the platinum.
A further exemplary embodiment of a radioactive brachytherapy source is shown and described in international patent application WO 94/25106. Therein is shown and described a nickel-titanium wire with a longitudinal, axially directed cavity at a tip. That cavity is filled with a number of iridium-192 spheres.
A still further embodiment of a radioactive brachytherapy source is shown and described in international patent application WO 92/00776. Therein is shown and described a source comparable to the source shown in U.S. Pat. No. 4,861,520, however, with a single elongated rod of radioactive material in place of a number of pellets.
Further embodiments of radioactive brachytherapy sources are shown and described in the United States Registry of Radioactive Encapsulated Sources and Devices. The Registry may be approached through the Internet at website                http://www.hsrd.ornl.gov/nrc/ssdr/ssdrindj.htm#J.K        
Registration No. LA-0557-S-102-S describes and shows an iridium wire encapsulated with a 3 micron titanium coating. The titanium coating forms a hard (flexible) shell around the Ir-192 wire. The Ir-192 wire is positioned and encapsulated inside a nickel/titanium tube that has a cavity formed by a nickel titanium wire that runs the entire length of the tube and stops short of the last 32 mm. This forms the cavity that accepts the 30 mm long Ir-192 wire. The backbone wire is welded to the distal end of the tube to form a tight seal. The Ir-192 wire is placed into the cavity created inside the tube and the proximal end of the tube is welded shut to firmly encapsulate the Ir-192 wire.
Registration No. LA-0760-S-102-S describes and shows a 10 mm long Ir-192 seed encapsulated firmly inside a solid titanium/nickel wire. The Ir-192 seed is inserted into a hole drilled into an end of the titanium/nickel wire.
Registration No. LA-0760-S-105-S describes and shows a P-32 source. A thin film of P-32 is deposited within a carrier tube. The carrier tube is inserted into a cylindrical cavity at an end of a nickel/titanium tube, which has been welded on a nickel/titanium wire. A tungsten wire marker is inserted into the tube at the distal end of the carrier tube. A nickel titanium plug is inserted in the distal tip of the tube cavity and then welded to form a seal.
Handbook of Vascular Brachytherapy, ed. Ron Waksman and Patrick W. Serruys, Martin Dunitz Ltd, 1998, London at pages 489-497 show a brachytherapy source delivery system in which a “train” of several miniature cylindrical encapsulated sources containing Sr-90/Y-90 is delivered to the angioplasty site through a catheter by means of a fluid.
Registration No. NR-569-S-101-S describes and shows encapsulated radioactive gold seeds. Each cylindrical seed contains a rod of gold, which is encased in a platinum sheath.
Registration No. GA-1061-S-101-S describes and shows a tube like source. The source is constructed by centering a platinum-iridium marker on the outer surface of a medical grade titanium inner tube, followed by a layer of Pd-103 suspended homogeneously in a water insoluble organic polymer matrix. The source is encapsulated by sliding an outer tube over the inner tube and laser welding both ends.
Registration No. NR-187-S-103-S describes and shows a substrate with adsorbed onto it either iodine-125 or cesium-131 or palladium-103 in liquid form. Substrates for iodine may be rods or balls of carbon, polytyrosine or an anion exchange resin. Also described is a solid piece of samarium-145. The source material is encapsulated in a cylindrical double-walled titanium capsule and encapsulated by laser weld.
Registration No. IL-136-S-338-S describes and shows iodine-125 absorbed on a solid silver bar and encapsulated in a cylindrical titanium capsule.
Registration No. IL-136-S-337-S describes and shows iodine-125 absorbed on anion exchange resin spheres and encapsulated in a cylindrical titanium capsule.
Registration No. CA0510S126S describes and shows palladium-103 electroplated on a metallic substrate or absorbed on ion exchange resin beads. The active element is then placed inside a titanium capsule, which is then welded on its ends to complete containment.
Depending on the type of tissue that has to be irradiated a choice for a radioactive isotope is to be made that is to be used in the radioactive brachytherapy source.
The above described and practically used sources make use of a multitude of isotopes.
Still more potential isotopes are described in U.S. Pat. No. 5,342,283. A considerable number of tables show for various desired beta- or gamma radiation outputs which isotopes of which elements produce such desired radiation. The patent is directed to coating pieces of a first material with one or more layers of second etc. materials.
U.S. Pat. No. 5,302,369 shows a method of manufacturing glass spheres containing a radioactive isotope. The glass spheres have diameters between 5 and 75 micron. First the glass spheres are manufactured such that they contain a precursor of the desired radioactive isotope. Thereafter the glass spheres are irradiated by neutron radiation to convert the precursor into the desired radioactive isotope. Other elements present in the glass spheres are selected from the group consisting of elements that do not become radioactive during neutron irradiation and elements that have a half life that is sufficiently short so that the other elements altogether do not emit a significant amount of beta- or gamma radiation at the time of administration of the radiation.
Radioactive brachytherapy source materials for incorporation in a radioactive brachytherapy source come in various shapes. Well known from the abovedescribed sources are spheres, microspheres, rods, pellets, cylindrically shaped, short rods, beads. Further known are ellipsoid like and lens like shapes.
In endovascular brachytherapy, especially for coronary applications, an encapsulated radioactive brachytherapy source is desired that can navigate short curves without getting stuck or piercing a catheter or vessel wall. Such a source preferably is not larger in diameter than about 1 mm. Consequently, the specific activity, i.e. the activity per unit mass, of the radioactive brachyhtherapy source material should be sufficiently high to allow the construction of a thin source with a sufficiently high source strength to limit treatment times to preferably no more than several minitues. Furthermore at least for certain endovascular brachytherapy applications a beta source may be desirable, i.e. a source that predominantly radiates beta radiation. Beta radiation has a relatively short range in tissue, i.e. the beta particles do not penetrate deeper into tissue than several millimeters. Thus an encapsulated radioactive brachytherapy source of beta radiation allows localized irradiation of the vessel wall without exposing oyther body parts of the patient to radiation. Furthermore radiation exposure of medical personnel residing close to the patient is minimized, allowing the irradiation procedure to be performed adjacent to the angioplasty procedure within the ordinary cathlab environment without need for extensive shielding. A problem encountered in beta radiation source materials used in practice is that the mean energy of the beta radiation of many radionuclides is on the low side for brachytherapy applications. Another problem encountered in beta radiation sources is a short half life. In fact, it is known from nuclear physics that generally the half life of beta emitting radionuclides is relatively short when the beta energy is high. Too short a half life results in logistics problems as a consequence of the fact that an installed source has to be replaced with a new source after a short period already. It is desired to produce the radioactive source material both economically and reliably. Reliability of supply is important to assure that decayed sources can be replaced in time and requires that the source material can be produced by means of readily available production facilities, including e.g. nuclear radio isotope production reactors.
Consequently, a need has remained for a radioactive brachytherapy source material that emits beta radiation of sufficiently high energy and has a sufficiently long half life, that can be produced at a sufficiently high specific activity to allow short treatment times that can be produced both economically and reliably and that will allow the construction of a thin, encapsulated radioactive brachytherapy source in which that material has been applied to navigate short curves in coronary vessels and that may also have applications in other brachytherapy fields.